The present invention relates to a heat treatment apparatus.
In general heat treatment apparatuses, reactive gas is introduced as the treatment gas into a treatment container for forming a thin film, such as an oxidation or nitrogenation film, on the surfaces of heat treatment objects, such as semiconductor wafers. Among widely used versions of these apparatus are those for performing oxidizing, CVD and diffusion treatment. Recently, the vertical type heat treatment apparatus is gaining favor due to its advantage of easily performing uniform heat treatment of the heat treatment objects.
However, in a conventional vertical heat treatment apparatus, for example, a plurality of heat treatment objects are supported horizontally by a boat and loaded into a heat treatment container and heated to the treatment temperature by a heating furnace. Treatment gas is then supplied to the container and heat treatment is performed for forming an oxidation or other type of thin film on the object surfaces. After film formation, the boat is unloaded from the container, and the objects are removed sequentially from the boat.
However, in view of the continuing trend toward higher integration and microminiaturization of semiconductor integrated circuits, in addition to the need for greater diameter of the treatment objects, the requirement has increased for performing uniform heat treatment in order to obtain unvarying film thickness throughout the treatment object surfaces.
In addition, due to the increasing demand for semiconductor integrated circuits, the need has grown for simultaneously treating a plurality of objects. For these reasons, uniform heating of the heating area in the heat treatment apparatus treatment container and uniform treatment gas density have both become major issues.
Various means for promoting uniform treatment gas density in a heat treatment apparatus have appeared in the past. For example, in Japanese Patent Laid-Open Publication No. 3-47531, a fluid diffusion apparatus comprising a porous structure and a treatment apparatus utilizing this fluid diffusion apparatus, in addition to a treatment apparatus utilizing an injector comprising a porous structure are disclosed. In these apparatuses, reaction gas is supplied to the porous fluid diffusion device or injector so as to uniformly emit reaction gas from microscopic holes of the porous structure into the treatment area.
Also, in Japanese Utility Model Laid-Open Publication No. 58-191635, a vertical chemical vapor deposition apparatus is disclosed wherein a gas insertion nozzle from a gas mixing vessel is divided among a plurality of holes, and the test material (treatment object) can be freely loaded and unloaded with respect to the supporting stand at a variable horizontal position. In this vertical chemical vapor deposition apparatus, the gas mixing vessel is installed at the upper direction of the supporting stand at a suitable position for gas mixing. The gas supplied from the nozzle is mixed at the upper part of the gas mixing vessel, and the mixed gas is uniformly emitted from a plurality of holes in the gas mixing vessel to the test material on the supporting stand.
However, in the above mentioned treatment apparatus of 3-47531, although the reactive gas can be uniformly emitted from the upper direction of the heat treatment objects supported in the heat treatment boat, since microscopic pores formed in the porous structure are used for gas emission holes, the reactive gas supply speed is slow. Particularly when the treatment objects are to be treated for a short time interval, as in the case of forming a gate oxidation thin film, at the gas supply rate from this type of porous structure, uniform coverage of the entire heating area by the treatment gas is difficult in a short time. Consequently, heat treatment is difficult to perform in a short time and at uniform gas density, and for this reason, the problem is encountered where variations in heat treatment arise according to the treatment object supporting position.
Also, in the case of heat treatment using the above mentioned injector, in addition to the above mentioned problem, heat of the uniform heating area is absorbed by the reactive gas in the injector. The temperature declines in proximity of the injector to disrupt the temperature distribution of the uniform heating area, thus leading to variations in film formation within the same treatment object.
In the vertical chemical vapor deposition apparatus of 58-191635, treatment gas can be supplied uniformly by the gas mixing vessel to the upper surface of the test material on the supporting stand. However, since nearly all the gas is emitted-toward the upper surface of the treatment object, when this gas mixing vessel is used for a heat treatment apparatus wherein a plurality of treatment objects are supported simultaneously over many steps in the vertical direction, nearly all of the emitted gas flow meets resistance from the treatment objects arranged at the upper end and time is required for the gas to uniformly reach the lower treatment objects. Consequently, there is a likelihood of inability to uniformly heat treat the objects in a short time.